The employment of magnetoresistive (MR) sensors for reading signals from media is well known. Such sensors read signals from the media by detecting a change in resistance of the sensor due to magnetic fields from the media. Many variations of MR sensors are known, such as anisotropic magnetoresistive (AMR) sensors, dual stripe magnetoresistive (DSMR) sensors, giant magnetoresistive (GMR) sensors, spin valve (SV) sensors, spin-dependent tunneling (SDT) sensors and dual spin valve (DSV) sensors.
Common to these sensors is the need to provide bias fields, both to eliminate noise and to facilitate signal readout. A known means for biasing the sensor involves abutting a permanent magnet to ends of the sensor, the magnet preferably forming a contiguous junction across plural sensor layers. Conductive leads, which may be separate from the biasing means, may also adjoin sensor layers along a contiguous junction.
In order to form a contiguous junction, a sensor is usually deposited in layers and then its border defined by masking and ion beam milling or etching (IBE), reactive ion etching (RIE) or the like. As noted in U.S. Pat. No. 6,198,608, ideally milling could be performed that directs an ion beam exactly perpendicular to the surface on which the MR sensors are being formed, resulting in blunt sensor ends that terminate at a ninety-degree angle to that surface.
The prior art notes some problems that would have been expected to increase as the junction angle becomes shallower. U.S. Pat. No. 6,198,608 states that a shallow slope would be expected to create inaccuracy in the width of the sensor, which ideally should match the width of magnetic tracks on the media, called the “track-width.” A shallow slope may also increase the length of the contiguous junction regions on both ends of the sensor to be comparable to or even greater than the width of the sensor between the contiguous junction regions, blurring images and causing off-track errors. A shallower angle of the border defining the contiguous junction might also denigrate the bias field provided to the sensor and complicate the sensor domain structures, so that noise would be increased. Overmilling of the sensor layers into an insulating read gap layer is a conventional approach to increasing the slope of the contiguous junction.